Utilizing the latest techniques in genetics, biochemistry, and mass spectroscopy, I will focus on a recently discovered transcription factor, the estrogen receptor associated protein 140 (ERAP140) to determine its specific role in genomic regulation, identify and characterize posttranslational modifications (PTMs) of this 3rotein to evaluate their modulation of genomic regulation in healthy and diseased states. It is our hypothesis that the transcriptional activation potential of ERAP140 and its role in breast cancer, and tamoxifen resistant breast cancer, is likely modulated by, as yet, undetermined PTM states of ERAP140. I will focus on three 3reast tumor cell lines (MCF-7, T47D, and MDA231) with different pathologies expressing very high levels of ERAP140. Utilizing chromatin immunoprecipitation (CHIP), DNA promoter microarray analysis, isotopic labeling, and proteomics analysis of ERAP140 and its PTM state I will identify correlations with its altered pattern of promoter specific macromolecular transcription complex formation. Site-directed mutagenesis of the identified ERAP140 PTM sites will be evaluated in transcription translation assays and protein interaction assays for the mechanism of action behind these patterns.